It is known that infrared detectors can be distrubed by electromagnetic radiation, particularly by radar ("Rev. Sci. Instrum 53(6) June 1982, 735-748). Special measures have to be taken for avoiding such disturbances.
It has been attempted to improve the "electromagnetic tolerance" of infrared seeker heads with infrared detector with respect to radar radiation by providing the optical element in the radiation in the path of rays of the seeker head, e.g. a dome or lens, with electrically conductive coatings. Also electrically conductive grid structures have been applied upon the optical elements in the path of rays (DE-A-36 32 252).
Both measures suffer from the disadvantage, that with the attenuation of the radar radiation the radiation utilized in the infrared seeker heads is also attenuated.
From EP-A-0, 198,549 an arrangement for limiting and homogenizing the visual field of detector elements of a mosaic detector is known, wherein the detector elements receive a utilized light flux from an observed visual field. Each of the detector elements is arranged on a cooled carrier in a vessel, which is evacuated or filled with a gas of small thermal conductivity. An arrangement of optical fibers, which are arranged on the cooled carrier and are transparent in the used spectral range, is arranged in the vessel in contact with the detector elements or at a small distance therefrom opposite a window transparent in this spectral range. Indeed these optical fibers serve as light guides for the infrared radiation but do not cause attenuation of radar radiation.
US-A-4,609,820 relates to an image detection device with a detector array for infrared. The influence of the thermal radiation from the environment is to be suppressed by a light stop, such that practically only radiation from the observed visual field impinges upon the detector array. The stray radiation, if it cannot be avoided, should affect the detector evenly over the whole area of the detector. With reference to FIG. 1 of US-A-4,609,820, it is explained that the radiation in the middle of an array detector is more intense than at the ends. According to the teaching of US-A-4,609,820 the light stop forms a grid-shaped shielding body for homogenizing the radiation over the length of the detector array. This grid structure has no light guiding function. DE-B-25,41,818 and DE-B-21,19,501 show an infrared radiation detector for homing heads. This infrared radiation detector has a single detector element. This detector element is arranged in a Dewar vessel. A rotating visual field is generated in an image plane by an imaging system comprising a concave mirror facing the visual field and a plane mirror, which receives the rays reflected from the concave mirror. A modulator disc is located in the image plane. The radiation passing through the modudlator disc is guided upon the detector element by a field lens and a conic radiation guide.
GB-A-2,198,878 shows a pyroelectric radiation detector, in which the surface exposed to radiation of a detector element made of radiation-sensitive material is provided with a radiation-absorbing electrode. The radiation-absorbing electrode has cutouts, which are in alignment with grooves in a radiation-sensitve material. The grooves have radiation-absorbing side walls. The depth of the grooves is in the order of mangitude of the wave length of the radiation to be detected. The width of the grooves is similarly dimensioned.
US-A-4,591,717 shows an infrared detector comprising a vacuum tube, in which a photosensitive layer is provided. The photosensitive layer has needles in the form of metal whiskers. These needles are closely packed and arranged perpendicular to a substrate.